1. Field of the Invention
The present invention relates to a layered structure of wire(s), a manufacturing method therefor, and a display apparatus including the layered structure of wire(s).
2. Description of the Related Art
Display apparatus using thin film transistors (hereinafter simply referred to as TFTs) as switching elements have been on the market these days. Recently organic electroluminescent (EL) display apparatus employing current-driven type organic light emitting diodes (hereinafter also referred to as OLED) that function as luminous elements are attracting attention as display apparatus to replace CRTs and LCDs. In display apparatus using organic electroluminescent (EL) elements, the TFTs are used also to drive the organic EL elements.
FIG. 5 is a cross-sectional view of a TFT in a display apparatus using an organic EL element. A TFT 200 has a stacked structure in the order of an insulating substrate 210 which is made of quartz glass or the like, an active layer 243 which is made of a polycrystalline silicon, a gate insulating film 212 which is made of SiO2 (silicon oxide), and a gate electrode 242 which is made of a refractory metal such as molybdenum (Mo). The active layer 243 is provided with a channel 243c below the gate electrode 242 and a drain 243d and a source 243s, both formed by ion injection with the gate electrode 242 as a mask, on both sides of the channel 243c. 
The TFT 200 further includes an interlayer insulating film 215 which comprises a first interlayer insulating film 213 made of SiN and a second interlayer insulating film 214 made of SiO2, a drain electrode 253 and a source electrode 254. The drain electrode 253 and the source electrode 254 are formed by filling aluminum (Al) or like metal in the contact holes provided corresponding to the drain 243d and the source 243s, respectively. The contact holes to be used in forming the drain electrode 253 and the source electrode 254 are formed by etching with buffered hydrofluoric acid or the like.
In the TFT 200 structured as described above, however, the first interlayer insulating film 213 is made of SiN which has a lower etching rate than SiO2 that constitutes the gate insulating film 212 therebelow when using buffered hydrofluoric acid. Thus, if the contact holes are formed by wet etching using the buffered hydrofluoric acid, an overhang, where more of the gate insulating film 212 is etched as shown in FIG. 6A, will be formed at the boundary between the gate insulating film 212 and the first interlayer insulating film 213. The formation of an overhang like this may cause a problem of increased contact resistance due to a level difference between the drain electrode 253 and the source electrode 254, which are formed by their respective contact holes.
With display apparatus using organic EL elements, on the other hand, the driver TFTs including layered structure of wire(s) which serves as a power supply line for the organic EL elements are required to have higher reliability, which is to be realized by such measures as lowering resistance, reducing whiskers and hillocks or eliminating electromigration or stressmigration. To lower the resistance, the drain electrode 253 and the source electrode 254 are structured of a low-resistance metal such as the above-mentioned aluminum. Moreover, whiskers and hillocks are reduced by providing a protective metal layer made of a refractory metal such as molybdenum, in such a manner as to cover the wiring layer made of a low-resistance metal such as aluminum. The protective metal layer like this is formed thinner than the wiring layer made of a low-resistance metal in order to reduce the resistance of the layered structure of wire(s) as a whole and to reduce the unevenness of the panel surface.
When the drain electrode 253 and the source electrode 254 are formed of a wiring layer of a low-resistance metal and a protective metal layer, there may arise a problem of the protective metal layer severed due to a level difference created by the overhang formed in the contact hole as shown in FIG. 6B. Moreover, as illustrated therein, a whisker may result at the severed portion. In particular, since the cathode of an organic EL element is formed all above the drain electrode 253 and the source electrode 254, the whisker sprouting on the upper protective metal layer will cause a short circuit between these electrodes and the cathode of the organic EL element, thus rendering the display apparatus defective.
The present invention has been made in view of the foregoing circumstances and an object thereof is to provide a layered structure of wire(s) capable of reducing the occurrence of defective display apparatus by preventing a short circuit between electrodes. Another object of the present invention is to reduce the occurrence of whiskers in the layered structure of wire(s). Still another object of the present invention is to lower the resistance of the layered structure of wire(s).
According to the present invention, there is provided a layered structure of wire(s) provided in a contact hole formed in an insulating film in which a first insulating layer and a second insulating layer made of different material from each other are stacked in this order, and this layered structure of wire(s) includes: a first metal layer which is made of a refractory metal; a wiring layer, formed on the first metal layer, which is made of a metal whose resistance is lower than that of the refractory metal; and a second metal layer, formed on the wiring layer, which is made of a refractory metal and is thicker than the first insulating layer.
By forming the second metal layer thicker than the first insulating layer, it is possible that the second metal layer is formed without the occurrence of any severance even when an overhang is formed at a boundary between the first and second insulating layers at the contact hole. As a result, the formation of whiskers on the second metal layer can be prevented, so that no short circuit is caused between this layered structure of wire(s) and other electrodes.
The first insulating layer may be made of SiO2 or SiON. Moreover, the second insulating layer may be made of SiN.
As the refractory metal, metal including a group 6A element such as molybdenum (Mo), chromium (Cr) or tungsten (W), for example, may be used. Provision of such a metal layer can contribute to reducing the occurrence of whiskers and hillocks in an interconnection structure. Moreover, these group 6A elements are characterized in that they exhibit less diffusion against the low-resistance metal. Furthermore, tantalum (Ta), vanadium (V) or niobium (Nb) may be used as the refractory metal. It is preferable that the refractory metal includes the molybdenum. In particular, the molybdenum can be processed with ease in its manufacturing process.
As a metal that constitutes the wiring layer, aluminum (Al), copper (Cu), silver (Ag), gold (Au), rhodium (Rh), iridium (Ir), nickel (Ni), platinum (Pt) or palladium (Pd) may be used, for example. The layered structure of wire(s) can be made low-resistant by using these metals as above. Among these metals, aluminum in particular, copper or silver whose resistivity is lower than that of aluminum is preferably used. It is particularly preferable that the wiring layer be made of metal including aluminum. Thereby, the adhesion of aluminum with the metal layer made of the refractory metal is enhanced because reactivity of aluminum is high, thus contributing to the improvement of a yield of the layered structure of wire(s).
According to the present invention, there is provided a layered structure of wire(s) provided in a contact hole formed in an insulating film in which a first insulating layer and a second insulating layer made of different material from each other are stacked in this order, and the layered structure of wire(s) includes: a first metal layer which is made of a refractory metal; a wiring layer, formed on the first metal layer, which is made of a metal whose resistance is lower than that of the refractory metal; and a second metal layer, formed on the wiring layer, which is made of a refractory metal and is so formed as to be thicker than a distance between an overhang and the first insulating layer therebelow, wherein the contact hole is formed by using a predetermined etchant, and in the second insulating film there is formed the overhang which is protruded beyond the first insulating film toward the center of the contact hole.
By forming the second metal layer thicker than the distance between the overhang formed on the second insulating film at the contact hole and the first insulating film therebelow, it is possible that the second metal layer is formed without the occurrence of any severance since the effect of the overhang will be thus absorbed. Thus, the formation of whiskers on the second metal layer can be prevented, so that no short circuit is caused between this layered structure of wire(s) and other electrodes. It is to be understood that the second metal layer in this case can be formed thicker than the distance between a tip of the overhang and the first insulating film therebelow.
A buffered hydrofluoric acid may be used as the predetermined etchant.
According to the present invention, there is provided a layered structure of wire(s) provided in a contact hole formed in an insulating film in which a first insulating layer and a second insulating layer made of different material from each other are stacked in this order, and the layered structure of wire(s) includes: a first metal layer which is made of a refractory metal; a wiring layer, formed on the first metal layer, which is made of a metal whose resistance is lower than that of the refractory metal; and a second metal layer, formed on the wiring layer, which is made of a refractory metal and is formed to have thickness such that any severance does not occur due to a level difference caused by different etching rates of the first insulating layer and the second insulating layer when using a predetermined etchant, wherein the contact hole is formed by using the predetermined etchant.
By forming the second metal layer accordingly, it is possible that the second metal layer is formed without the occurrence of any severance. Thus, the formation of whiskers on the second metal layer can be prevented, so that no short circuit is caused between this layered structure of wire(s) and other electrodes.
The contact hole may be formed in such a manner that the second insulating layer has a taper slower than that of the first insulating layer.
By forming the taper of the second insulating layer slower than that of the first insulating layer, the effect of the overhang can be reduced, so that the thickness of the second metal layer can be made smaller. Thus, the layered structure of wire(s) can be made low-resistant.
The insulating film may further include a third insulating layer, formed on the second insulating layer, which is made of material whose etching rate is greater than that of the second insulating layer when using the predetermined etchant. In a case when the second insulating layer is SiN, the third insulating layer may be made of SiO2 or SiON. By providing another insulating layer such as the third insulating layer described above, the third insulating layer is etched faster than the second insulating layer during etching, so that the second insulating layer is also etched from the above and the taper of the second insulating layer can be made looser.
The second insulating layer may be formed such that the thickness of the second insulating layer is greater than or equal to that of the first insulating layer and is less than or equal to approximately 600 nm.
By forming the second insulating layer in a manner such that the thickness of the second insulating layer is greater than or equal to the thickness of the first insulating layer, the taper of the second insulating layer can be made looser than that of the first insulating layer. Moreover, by forming the second insulating layer in a manner such that the thickness thereof is less than or equal to 600 nm, etching time required for the formation of the contact hole can be controlled, so that spreading of the contact hole can be properly restricted.
The first metal layer can be formed thicker than the first insulating layer. By forming the first metal layer thicker than the first insulating layer, it is possible that the first metal layer is formed without the occurrence of any severance even when the overhang is formed at the boundary between the first and second insulating layers at the contact hole. As a result, the formation of whiskers on the first metal layer can be prevented, so that no short circuit is caused between this layered structure of wire(s) and other electrodes.
The above-described layered structure of wire(s) can be used for a semiconductor device including a semiconductor layer provided between a substrate and the first insulation layer, and a gate electrode provided in a position different from a spot where the contact hole is formed over the first insulating layer. In that case, the first insulating layer functions as a gate insulating film, and the second insulating layer functions as a gate insulating film or an interlayer insulating film. The contact hole may be formed in such a manner that the first and second insulating layers are penetrated through by the contact hole in order that the layered structure of wire(s) is connected to the semiconductor layer.
According to the present invention, there is provided a method of manufacturing a layered structure of wire(s), and the method comprises: forming a contact hole in an insulating film in which a first insulating layer and a second insulating layer made of different material from each other are stacked in this order, by etching with a predetermined etchant; forming a first metal layer which is made of a refractory metal, in the contact hole; forming a wiring layer, on the first metal layer, which is made of a metal whose resistance is lower than that of the refractory metal; and forming a second metal layer made of a refractory metal, on the wiring layer, so as to be thicker than the first insulating layer.
The forming the contact hole may be such that the etching is performed by using an etchant whose etching rate for the first insulating layer is higher than that for the second insulating layer.
According to the present invention, there is provided a display apparatus which includes any one of the layered structure of wire(s) described above and an optical element having at least an anode, a luminous element layer and a cathode that are provided above the layered structure of wire(s).
According to the present invention, there is provided a display apparatus which includes: a layered structure of wire(s) provided in a contact hole formed in an insulating film in which a first insulating layer and a second insulating layer made of different material from each other are stacked in this order; and an optical element, formed over the layered structure of wire(s), which has at least an anode, a luminous element layer and a cathode, wherein the layered structure of wire(s) includes: a first metal layer which is made of a refractory metal; a wiring layer, formed on the first metal layer, which is made of a metal whose resistance is lower than that of the refractory metal; and a second metal layer, formed on the wiring layer, which is formed to be thicker than the first insulating layer.
By forming the second metal layer thicker than the first insulating layer, it is possible that the second metal layer is formed without the occurrence of any severance even when an overhang is formed at the boundary between the first and second insulating layers at the contact hole. As a result, the formation of whiskers on the second metal layer can be prevented, so that no short circuit is caused between this layered structure of wire(s) and an electrode of the optical element provided thereabove. Especially when the cathode of the optical element is formed commonly for a plurality of pixels of the display apparatus, the prevention of short circuit between the layered structure of wire(s) and the cathode can significantly reduce the probability of the display apparatus rendered defective.
It is to be noted that any arbitrary combination of the above-described structural components, and expressions changed between a method and an apparatus are all effective as and encompassed by the present embodiments.
Moreover, this summary of the invention does not necessarily describe all necessary features so that the invention may also be sub-combination of these described features.